In some internal combustion engine applications, liquid propane injection can provide some potential benefits relative to gaseous propane injection in ether port fuel injection or direct fuel injection systems. As one example, liquid propane injection provides reduced air displacement that allows for increased air mass to enter an engine cylinder resulting in increased volumetric efficiency relative to gaseous propane injection.
A typical liquid injection propane fuel system for an internal combustion engine supplies liquid propane from a pressurized tank via a fuel pump to a fuel rail. The liquid propane is injected from the fuel rail to cylinders of the internal combustion engine via fuel injectors. Excess fuel can be returned to the pressurized tank during operation via a pressure relief supply line.
However, the inventor has recognized several potential issues with such liquid propane fuel systems. For example, during engine shut-off conditions, fuel rail pressure is reduced so that propane cannot be pumped back to the fuel tank via the pressure relief supply line and instead resides in the fuel rail. The liquid propane residing in the fuel rail during engine shut-off conditions may evaporate and leak out of the fuel rail via the fuel injectors into the atmosphere causing increased emissions and reduced fuel economy.
In one example, the above mentioned issues may be addressed by a method for controlling fuel flow in a vehicle. The method may comprise during a first mode of operation, directing fuel from a fuel rail to a fuel tank, and during a second mode of operation, directing fuel from the fuel rail to a fuel vapor canister.
As an example, the first and second mode may be performed during a vehicle shut-off condition in order to evacuate fuel from the fuel rail. By operating in the first mode, liquid fuel may be evacuated from the fuel rail and returned to the fuel tank. In particular, at vehicle shut-off a fuel rail pressure may be significantly higher than a fuel tank pressure. This pressure difference forces liquid fuel from the fuel rail to the fuel tank. As the liquid fuel evacuates from the fuel rail, the remaining fuel evaporates into gaseous fuel causing a drop in pressure which stops evacuation of the liquid fuel. Accordingly, by operating in the second mode, the remaining gaseous fuel can be directed to the fuel vapor canister. In this way, evaporative emissions resulting from fuel in the fuel rail evaporating and leaking out of the fuel injectors can be reduced and fuel economy can be increased.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this description.